The present invention relates to artillery projectiles in general and specifically to a device for correcting the range and deflection errors inherent in an unguided spin stabilized projectile.
There is need to improve the accuracy of artillery shells fired by large bore weapons. Technological advances in metallurgy, propulsion, guidance and control now make it feasible for artillery systems to attack targets at ranges greater than 20 miles. Artillery shells, follow a ballistic trajectory, which in an ideal world can be determined mathematically from launch point to target. However, the real world is not as forgiving. Numerous factors affect the trajectory. Variations in temperature, wind and precipitation along with minute differences in manufacturing tolerances of the projectile, the barrel of the weapon, and the charge are just a few of the factors affecting the flight of a projectile. Moreover, there is typically no control of the projectile after launch. Therefore, as the range increases, the potential impact footprint of the projectile grows until it reaches the point where the projectile can no longer be relied upon to accomplish the desired mission.
There is a need then to improve the accuracy of artillery projectiles through in-flight control. One proposed solution addressed by prior art is the smart projectile, which is basically a gun-fired guided missile. These weapons are extremely complex. In addition to the normal fuze and payload found in unguided projectiles, these weapons utilize Inertial Measuring Units (IMUs) containing gyros and accelerometers, complex canard assemblies with actuator motors and drive electronics and/or variable angle rocket nozzles, and long grain rocket motors with complex finned base assemblies.
The complexity of a smart projectile results in reliability issues. The delicate components of these projectiles are subject to failure due to the high acceleration pressure, temperatures and rotational velocities experienced throughout launch and the flight. The projectile may have to be de-spun prior to flight correction in order to protect the internal components from the high rotational velocities imparted from the rifled barrels. Furthermore, accuracy in such weapons comes at a high cost. Fully guided rounds such as ERGM, XM982 and AGS LRLAP cost between $25,000.00 to $80,000.00 a piece. While simpler, less expensive corrector designs have been proposed, none provide the required two dimensions of control for range and deflection errors.
There is a further need then to efficiently utilize the inventory of current artillery pieces. Improvements to the projectile must be compatible with existing rounds. Modem artillery barrels are rifled so as to create spin in the projectile. Without spinning, the projectile has a tendency to tumble which makes it impossible to determine with any level of confidence where the projectile is going to land. One consequence of spin is that it creates a yawing to the right (with right hand refilling twist) or side slip angle called the yaw of repose. When a projectile is fired at a range of 20 miles, the yaw of repose will result in a cross range deflection of about 1 mile. In order to continue using existing weapon systems with rifled barrels, the proposed system must be able to compensate for the affects of rifling.
What is needed is a system that can provide two dimensional in-flight projectile trajectory correction more simply and less expensively than a guided projectile. Preferably the system can be used to modify the millions of artillery rounds in the existing inventory or be simply added to new artillery rounds. The system should be safe from electronic jamming, which is likely in a combat environment. The system should improve accuracy so that the corrected projectiles can be used effectively for targets at ranges in excess of 20 miles.
The present invention is a two dimensional (2-D) projectile trajectory corrector system for placement on an artillery projectile that includes multiple aerodynamic surfaces which affect drag and spin so that range and cross range deflection may be adjusted in-flight through a deployment method that may include vernier corrections. The two dimensional projectile trajectory corrector system also contains means for receiving positional data and a programmable timer for implementing the deployment strategy necessary for trajectory adjustment.